Symbol: Something that on the surface is its literal self but which also has another meaning or even several meanings. A symbol may be said to embody an idea. There are two types of symbols: symbols that embody universally recognizable meanings and constructed symbols that are given symbolic meaning by the way an author uses them in a literary work. In more psychological and philosophical terms, all concepts are symbolic in nature and representations for these concepts are simply token artifacts that are allegorical to a symbolic meaning. Symbols are objects, characters, figures, or colors used to represent abstract ideas or concepts.

Shakespeare –

In Hamlet Shakespeare uses Flowers to symbolize purity and also to represent character traits and all that Ophelia has lost when she gives the flowers away.
The following are interpretations of flower meanings:
Rosemary Remembrance, usually at at funerals, but sometimes remembrance between lovers (Ophelia could give this to Hamlet as foreshadowing or as a symbol of why she is now mad).
Pansies Thought (Thought in French is Pensees and to think in Spanish is Pensar (Word-play --> symbol (like how four is unlucky in Chinese because it sounds like death). Would also work for Hamlet, but it could also work for Horatio
Fennel Marital Infidelity. For Gertrude or Claudius
Columbines Flatery or insincerity culminating in ingratitude, and thanklessness. For Claudius
Rue (Herb of Grace) Repentance or sorrow. For Claudius (repent sins) or Laertes (sorrow over father's death)
Daisy Forsaken Love, Unhappy love. Gertrude or Hamlet
Violets Faithfulness. Hamlet, Claudius or Gertrude (There are no violets any more (loyalty and fidelity is gone))

If you believe that Ophelia's death was purposeful (she didn't slip and drown by accident) then your claim can be backed up with Pansies and Rosemary (she's making sure that they know to remember her and why she died)

Skull
The skull that Hamlet holds up is just a skull, but also represents the brief futility of life. The skull is a reminder of death, a symbol of the physical breakdown after death and a sign that death is inevitable to all. Hamlet comes across the skull, which fuels his fascination with the consequences of death – final and physical. This reminder of loss and Hamlet's willingness to face it is symbolic of his acceptance of loss as both part of life and as the end of life.

Frost

In Robert Frost's poem "Mending Wall" the wall that the narrator and his neighbor build represent the divide between people as well as the decision to build up tradition or to renew it and make it fit in the contemporary world.
In "Stopping by Woods on a Snowy Night", the woods are a symbol of an escape from normal, chaotic every day life, where the narrator can calm down and relax before going back out into the "real world".


en.wikipedia.org/wiki/Symbol
http://www.virtualsalt.com/litterms.htm